I=U/R

U: voltage, v;

R: resistance, ω;

I: current, a;

2, the whole circuit ohm's law:

I=E/(R+r)

I: current, a;

E: electromotive force of power supply, v;

R: internal resistance of power supply, ω;

R: load resistance, ω

3, series circuit, the total voltage is equal to the sum of the voltages on each resistor.

U=U 1+U2+…Un

4, parallel circuit, the total voltage is equal to the voltage.

U=U 1=U2=U3=…=Un

5. Power of the load

Pure resistance active power P=UI → P=U2/R (where 2 is the square)

U: voltage, v;

I: current, a;

P: active power, w.

Voltage, also called potential difference or potential difference, is a physical quantity to measure the energy difference of unit charge in electrostatic field due to different potentials. Its magnitude is equal to the work done by the unit positive charge moving from point A to point B under the action of electric field force, and the direction of voltage is defined as the direction from high potential to low potential.

The international unit system of voltage is volts (V for short), and commonly used units are millivolts (mV), microvolts (μV) and kilovolts (kV). This concept is similar to the "water pressure" caused by the high and low water level. It should be pointed out that the word "voltage" is generally only used for circuits, while "potential difference" and "potential difference" are generally used for all electrical phenomena.

Voltage is the reason that drives the directional movement of charge to form current. The reason why current can flow in the wire is also because there is a difference between high potential and low potential in the current.